Device and method for transmitting downlink control information in a wireless communication system

ABSTRACT

A method for a transmitter in a communication system, a method for a receiver, a transmitting apparatus, and a receiving apparatus are provided. The method includes identifying, by a transmitter, information bits in a first downlink control information (DCI) and information bits in a second DCI; appending, by the transmitter, one bit of value zero to the second DCI, if a number of the information bits in the second DCI is equal to a number of the information bits in the first DCI; appending, by the transmitter, one or more zero bits to the second DCI based on a payload size of the second DCI, if the number of the information bits in the second DCI belongs to one of ambiguous sizes; and transmitting, to a receiver, the second DCI, wherein a payload of the second DCI comprises the information bits in the second DCI and at least one zero padding bit appended to the second DCI, and wherein the one or more zero bits is appended to the second DCI until the payload size of the second DCI does not belong to one of the ambiguous sizes and the payload size of the second DCI is not equal to a payload size of the first DCI.

PRIORITY

This application is a Continuation Application of U.S. patentapplication Ser. No. 12/610,849, filed in the U.S. Patent and TrademarkOffice on Nov. 2, 2009, and is now issued as U.S. Pat. No. 9,461,856 onOct. 4, 2016, which claims priority to a Korean Patent Application filedin the Korean Intellectual Property Office on Oct. 31, 2008 and assignedSerial No. 10-2008-0107684, the entire content of each of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a wireless communicationsystem and, in particular, to a device and method for transmittingdownlink control information in a wireless communication system in whichthe control information including downlink data transmissioninformation, uplink resource allocation information, and transmissionpower control information is carried by a Physical Downlink ControlChannel (PDCCH).

2. Description of the Related Art

In Long Term Evolution (LTE), multiple Downlink Control Information(DCI) formats are specified to support various transmission modes, and aUser Equipment (UE) decodes the DCI using a blind decoding, wherein theDCI format type is determined by the size of the DCI format payload,rather than from any format identifier. Accordingly, the DCI formatshave different sizes of payloads. The DCI formats include format 0,format 1, format 1A, etc. Therefore, when the DCI formats have the samesize payload, the UE may fail to identify the DCI format correctly, andsubsequently cannot decode the DCI.

In a conventional method for determining the payload size, the payloadsizes of the DCI format 0 (N₀) and DCI format 1A (N_(1A)) are firstdetermined and then the payload size of the DCI format 1 (N₁) isdetermined. The payload size of the DCI format 1 is determined dependingon the downlink bandwidth (i.e., a number of Resource Blocks (RBs)) andduplex mode, and by excluding padding bits and 16-bit UE identifier.

The DCI format 1 must have a payload size different from that of the DCIformat 0/1A. If the number of information bits in DCI format 1 is equalto that in the DCI format 0/1A, a padding bit is appended to the DCIformat 1 so as to update the N₁=N₁+1.

However, if the updated payload size of the DCI format 1 is an ambiguoussize, another padding bit is appended to the DCI format 1 and N_(1A) isincremented by 1. If the payload size of the DCI format 1 is not anambiguous size, no further padding bits are necessary, and the payloadsize N₁ of the DCI format 1 is determined.

However, the conventional DCI format 1 payload size determination methodhas a drawback in that the payload size of the DCI format 1 can be equalto that of another DCI format. As described above, a padding bit isappended to the DCI format 1 to differentiate the payload size of theDCI format 1 from that of the DCI format 0/1A, and another padding bitis further appended to the DCI format 1 such that the payload size ofthe DCI format 1 is not an ambiguous size. Therefore, although thepayload size N₁ of the DCI format is differentiated from payload size N₀of the DCI format 0, they may end up being equal to each other as aresult of appending the padding bit to avoid the payload size N₁ frombelonging an ambiguous size.

For example, assuming that N₀ and N₁ have a relationship of N₁=N₀−1, thepadding bit addition step is skipped because N₀ and N₁ have differentvalues and, consequently, the relationship of N₁=N₀−1 is maintained.However, if N₁ is an ambiguous size, a padding bit subsequently isappended to the DCI format 1 such that the N₁ increments by 1 (N₁+1),resulting in N₀=N₁.

Such a problem occurs when N_(RB) ^(DL)=30 and N_(RB) ^(UL)=6 in aFrequency Division Duplexing (FDD) mode. In this situation, the payloadsize of both the DCI format 0 and DCI format 1A is 25 bits and thepayload size of the DCI format 1 is also 25 bits. Because the DCI format1 cannot be differentiated from the DCI format 0/1A, based on thepayload size, the UE fails to differentiate the two DCI formats in sucha problematic situation, and Physical Downlink Control Channel (PDCCH)decoding fails.

SUMMARY OF THE INVENTION

In order to address at least the above-described problems of the priorart, in accordance with an embodiment of the present invention, a deviceand method are provided for transmitting downlink control information ina wireless communication system that is capable of differentiatingpayload sizes of different DCI formats from each other by introducing animproved padding bit addition algorithm.

Further, a device and method are provided for transmitting downlinkcontrol information in a wireless communication system that is capableof differentiating a payload size of a DCI format 1 from a payload sizeof the preset DCI format 0/1A.

In accordance with an embodiment of the present invention, a method fora transmitter in a communication system is provided. The method includesidentifying, by a transmitter, information bits in a first downlinkcontrol information (DCI) and information bits in a second DCI;appending, by the transmitter, one bit of value zero to the second DCI,if a number of the information bits in the second DCI is equal to anumber of the information bits in the first DCI; appending, by thetransmitter, one or more zero bits to the second DCI based on a payloadsize of the second DCI, if the number of the information bits in thesecond DCI belongs to one of ambiguous sizes; and transmitting, to areceiver, the second DCI, wherein a payload of the second DCI comprisesthe information bits in the second DCI and at least one zero padding bitappended to the second DCI, and wherein the one or more zero bits isappended to the second DCI until the payload size of the second DCI doesnot belong to one of the ambiguous sizes and the payload size of thesecond DCI is not equal to a payload size of the first DCI.

In accordance with another embodiment of the present invention, a methodfor a receiver in a communication system is provided. The methodincludes receiving, by a receiver from a transmitter, controlinformation comprising at least one of a first downlink controlinformation (DCI) and a second DCI; and decoding, by the receiver, thecontrol information based on a payload size of the second DCI, whereinone bit of value zero is appended to the second DCI by the transmitter,if a number of information bits in the second DCI is equal to a numberof information bits in the first DCI, wherein a payload of the secondDCI comprises the information bits in the second DCI and at least onezero padding bit appended to the second DCI, wherein one or more zerobits is appended to the second DCI based on the payload size of thesecond DCI by the transmitter, if the number of the information bits inthe second DCI belongs to one of ambiguous sizes, and wherein the one ormore zero bits is appended to the second DCI until the payload size ofthe second DCI does not belong to one of the ambiguous sizes and thepayload size of the second DCI is not equal to a payload size of thefirst DCI.

In accordance with another embodiment of the present invention, atransmitting apparatus in a communication system is provided. Theapparatus includes a transmitter for transmitting a signal to areceiver; and a controller configured to: identify information bits in afirst downlink control information (DCI) and information bits in asecond DCI, append one bit of value zero to the second DCI, if a numberof the information bits in the second DCI is equal to a number of theinformation bits in the first DCI, append one or more zero bits to thesecond DCI based on a payload size of the second DCI, if the number ofthe information bits in the second DCI belongs to one of ambiguoussizes, and transmit, to a receiver, the second DCI, wherein a payload ofthe second DCI comprises the information bits in the second DCI and atleast one zero padding bit appended to the second DCI, and wherein theone or more zero bits is appended to the second DCI until the payloadsize of the second DCI does not belong to one of the ambiguous sizes andthe payload size of the second DCI is not equal to a payload size of thefirst DCI.

In accordance with another embodiment of the present invention, areceiving apparatus in a communication system is provided. The apparatusincludes a receiver for receiving a signal from a transmitter; and acontroller configured to: receive, from a transmitter, controlinformation comprising at least one of a first downlink controlinformation (DCI) and a second DCI, and decode the control informationbased on a payload size of the second DCI, wherein one bit of value zerois appended to the second DCI by the transmitter, if a number ofinformation bits in the second DCI is equal to a number of informationbits in the first DCI, wherein a payload of the second DCI comprises theinformation bits in the second DCI and at least one zero padding bitappended to the second DCI, wherein one or more zero bits is appended tothe second DCI based on the payload size of the second DCI by thetransmitter, if the number of the information bits in the second DCIbelongs to one of ambiguous sizes, and wherein the one or more zero bitsis appended to the second DCI until the payload size of the second DCIdoes not belong to one of the ambiguous sizes and the payload size ofthe second DCI is not equal to a payload size of the first DCI.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentinvention will be more apparent from the following detailed descriptionin conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram illustrating a compressed resource allocationexpression method for 6 RBs according to an embodiment of the presentinvention;

FIG. 2 is a diagram illustrating a principle of a group resourceallocation method supported in DCI format 1 according to an embodimentof the present invention;

FIG. 3 is a flowchart illustrating a procedure of determining payloadsizes of DCI formats 0, 1, and 1A in a downlink control informationtransmission method according to an embodiment of the present invention;

FIG. 4 is a flowchart illustrating a procedure of determining a payloadsize of DCI format 1 in a downlink control information transmissionmethod according to an embodiment of the present invention;

FIG. 5 is a block diagram illustrating a configuration of a downlinkcontrol channel transmitter of a base station in a wirelesscommunication system according to an embodiment of the presentinvention; and

FIG. 6 is a block diagram illustrating a configuration of a downlinkcontrol channel receiver of a UE in a wireless communication systemaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Several embodiments of the present invention are described in detailbelow with reference to the accompanying drawings. The same referencenumbers are used throughout the drawings to refer to the same or likeparts. Additionally, detailed descriptions of well-known functions andstructures incorporated herein may be omitted to avoid obscuring thesubject matter of the present invention.

As described above, in an LTE system, several Downlink ControlInformation (DCI) formats are defined to support different communicationmodes. A UE receives the DCI and performs blind decoding thereon withoutan explicit format identifier, and subsequently identifies the DCIformat as a result of the blind decoding. The blind decoding isperformed under an assumption that the different DCI formats havedifferent payload sizes.

In accordance with an embodiment of the present invention, an improvedalgorithm for determining a number of padding bits to be appended to theDCI format to differentiate payload sizes of the distinctive DCI formatsis described below.

Using Adaptive Modulation and Coding (AMC) and channel adaptivescheduling, a base station can allocate the resources including thefrequency, time, and power based on the channel conditions of multipleusers. The adaptive resource allocation information is transmitted froma base station to the UE through a Physical Downlink Control Channel(PDCCH) such that the UE can recognize the radio resources allocatedthereto.

The PDCCH is used to carry the Downlink Control Information (DCI).

First, the DCI for Downlink resource allocation (hereinafter called“DL-DCI”) will be described.

The downlink resource allocation is adaptively performed based on thechanging channel conditions fed back by a corresponding UE and an amountof information to be transmitted to the UE. The PDCCH carries theinformation on the resource allocated to the corresponding UE fortransmitting the data and modulation and coding schemes. The UErecognizes the resource allocated to itself and how to decode the datadelivered within the resource based on the information carried by thePDCCH. A Cell Radio Network Temporary Identifier (C-RNTI) is a UEidentifier used to uniquely identify a UE such that the UE can identifythe signal destined to itself by checking the C-RNTI of the signal. TheC-RNTI is implicitly encoded in the Cyclic Redundancy Check (CRC)attached to the downlink control information. Accordingly, if the DLcontrol information is successfully decoded, the DL control informationis destined to the UE.

Second, the DCI for Uplink resource allocation (hereinafter called“UL-DCI) will be described.

The base station makes scheduling decisions based on the uplink channelquality acquired from a sounding reference signal transmitted by the UEand determines an amount of data to be transmitted based on a UE bufferstatus report. The uplink resource allocation is performed based on theUL channel quality and the amount of data to be transmitted to the UE.The PDCCH carries the information on the uplink resource allocated tothe UE and modulation and coding scheme to be used for the uplinktransmission. The UE recognizes the uplink resource allocated to itselfand how to encode the data to be transmitted within the uplink resource,based on the information carried by the PDCCH. Additionally, thededicated uplink control information is identified using the C-RNTI asthe dedicated downlink control information.

The PDCCH for DL-DCI includes the C-RNTI of the UE, Downlink ResourceBlock (DL RB) allocation information, Modulation and Coding Scheme (MCS)information, and Hybrid Automatic Repeat Request (HARQ) information.Regarding the DL RB information, if the DL control information isdecoded successfully, the UE can identify the RBs on which the downlinktransmission has been scheduled.

Regarding the MCS information, when the AMC algorithm is used in thesystem, the UE must know the MCS to perform demodulation and decoding onthe received signal.

Regarding the HARQ information, the HARQ information indicates whetherthe packet transmitted by the base station is successfully received bythe UE such that the base station transmits a next packet in response toa positive HARQ feedback and retransmits the previous packet in responseto a negative HARQ feedback. The HARQ information includes a New DataIndicator (NDI) for indicating a new data transmission and a RedundancyVersion (RV) when using the Incremental Redundancy (IR). The UEdetermines whether to combine the previously received packet beforedecoding or initialize a new decoding session.

The PDCCH for DL-DCI can further include the additional informationrelated to the multiple antenna transmission, power control, anddistributed RB assignment.

The PDCCH for UL-DCI includes C-RNTI, uplink RB assignment information,Modulation and Coding Scheme (MCS) information, and HARQ information.

For UL RB assignment, if the control information is decodedsuccessfully, the UE can identify the RBs on which the uplink data hasbeen scheduled.

Regarding the MCS information, when the AMC algorithm is used in thesystem, the UE must know the MCS to generate the uplink signal based onthe MCS informed by the base station. The PDCCH for UL-DCI can furtherinclude additional information related to an uplink Reference Signal(RS) for supporting Space Domain Multiple Access (SDMA), distributed RBassignment, and channel quality information request.

The number of information bits included in a PDCCH is determinedaccording to the control information carried by the PDCCH. For example,because the PDCCH for the DL-DCI and the PDCCH for the UL-DCI carrydifferent information, their sizes differ from each other.

As another example, the PDCCH for the DL-DCI carrying SpatialMultiplexing (SM) information also contains multiple MCS indicators andHARQ indicators for multiple packet transmissions on a samefrequency-time resource. Accordingly, the PDCCH for DL-DCI carrying theSM information is larger than the PDCCH for normal DL-DCI.

In order to differentiate the PDCCHs carrying different controlinformation, several DCI formats are defined. Further, because thePDCCHs carrying different information have different sizes, the UE candecode the potentially transmitted DCI and, if the DCI has beensuccessfully decoded, recognize which DCI format is transmitted, withoutusing a format identifier.

Table 1 below shows DCI format types specified in 3GPP LTE standards.

TABLE 1 DCI format Usage Size (number of bits) 0 UL-DCI Equal to format1A, 3, and 3A 1 DL-DCI No format equal in size 1A DL-DCI for compressedRB Equal to format 0, 3, assignment information and 3A 1B DL-DCI forprecoding information No format equal in size and compressed RBassignment information 1C DL-DCI for shared control No format equal insize information 1D DL-DCI for SM and compressed No format equal in sizeRB assignment information 2 DL-DCI for closed-loop SM No format equal insize information 2A DL-DCI for open-loop SM No format equal in sizeinformation 3 2-bit TPC command Equal to format 0, 1A, and 3A 3A 1-bitTPC command Equal to format 0, 1A, and 3

As shown in Table 1, some DCI formats are the same size and others arenot. For example, the formats 0, 1A, 3, and 3A are the same size.Accordingly, these formats cannot be differentiated based on formatsize.

However, the formats 0 and 1A can be differentiated with adifferentiation flag. Because the format 0 carries UL-DCI and the format1A carries DL-DCI, the UE identity information is contained therein.Meanwhile, the formats 3 and 3A are used to transmit transmission powercontrol information multiplexed for multiple UEs so as to contain theTPC-RNTI rather than C-RNTI. Accordingly, the formats 0, 1A, 3, and 3Acan be differentiated using the RNTI information. The formats 3 and 3Aare selectively used for a given UE according to the determination byhigher layers. Basically, there is no need to differentiate the formats3 and 3A because these formats are not received simultaneously.

Although no format identifier is needed when the DCI formats aredifferent in size, the UE still attempts decoding under an assumption ofpotential DCI formats, thereby increasing reception complexity. When allthe DCI formats are the same size, the reception complexity decreasesbut the additional format identifiers increase the amount of transmittedinformation.

Table 2 below shows information fields of the DCI format 0 specified in3GPP LTE standards.

TABLE 2 Field Number of bits C-RNTI 16 Format 0/format 1Adifferentiation 1 flag Frequency hopping flag 1 Resource allocation$\left\lceil {\log_{2}\left( \frac{N_{RB}^{UL}\left( {N_{RB}^{UL} + 1} \right)}{2} \right)} \right\rceil$MCS and RV 5 NDI 1 TPC 2 Cyclic shit for DM RS 3 UL subframe index 0 inFDD mode, 2 in TDD mode CQI request 1 Padding bits appended to format Z₀1A

In Table 2, the format 0/format 1A differentiation flag is 1 bit, whichis set to 0 to indicate format 0 and set to 1 to indicate format 1A. Thefrequency hopping flag is 1 bit that is set to 1 to instruct the UE toperform Physical Uplink Shared Channel (PUSCH) frequency hopping and setto 0 when there is no PUCH frequency hopping. It is preferable to enablefrequency hopping to achieve diversity gain and disable frequencyhopping to achieve AMC gain. Because the uplink data transmission isperformed with a synchronous HARQ, the integrated 5-bit MCS and RV fieldis defined to inform the UE of the modulation and coding scheme andredundancy version for uplink transmission.

The cyclic shift for DM RS is 3 bits for uplink Space Division MultipleAccess (SDMA) and indicates the orthogonal RS patterns for the UEsassigned the same RBs.

The UL subframe index is 2 bits, which are presented only for TDDoperation, and not for FDD operation. Unlike the FDD operation mode inwhich constant uplink and downlink resources are allocated, the uplinkand downlink is switched in the TDD mode. Because the uplink anddownlink resources can be allocated asynchronously in the TDD mode, theresource allocation for multiple uplink subframes should be allowed witha single downlink subframe. Further, because the resources should beidentified in both the frequency and time directions, the UL subframeindex is used to indicate subframe in time direction.

In LTE, the Channel Quality Indicator (CQI) report is transmittednon-periodically and multiplexed with the uplink data to be transmitted.The CQI request flag is 1 bit and is used to indicate whether or not theUE periodically transmits the CQI.

In Table 2, the number of bits in the resource allocation field of theDCI format 0 is based on the uplink bandwidth. The bandwidth isexpressed by a number of RBs in LTE. When the number of uplink RBs isN_(RB) ^(UL), the resource allocation field is set to |log₂ (N_(RB)^(UL)(N_(RB) ^(UL)+1)/2)|

In LTE, an Orthogonal Frequency Division Multiple Access (OFDMA) schemeis used for downlink transmission, and Single Carrier Frequency DivisionMultiple Access (SC-FDMA), which is a low Peak to Average Power Ration(PAPR) scheme compared to OFDMA, is used for uplink transmission. Inorder to maintain the low PAPR, the transmission should be performed onconsecutive RBs. That is, the signal transmitted on non-consecutive RBsusing the SC-FDMA scheme increases PAPR. The resource allocationreflecting such resource allocation constraint can be expressed asillustrated in FIG. 1.

More specifically, FIG. 1 is a diagram illustrating a compressedresource allocation expression method under an assumption of 6 RBs.

Referring to FIG. 1, the number of cases with 6 RBs (RB0 10, RB1 11, RB212, RB3 13, RB4 14, and RB5 15) is 5 for one RB, 4 for two RBs, 3 forthree RBs, 3 for four RBs, 2 for 5 RBs, and 1 for 6 RBs. The number ofcases can be explained with reference to the graph of FIG. 1. Node 51denotes the case where only the RB0 10 is selected. Node 53 denotes thecase where the RB3 13, RB4 14, and RB5 15, indicated by its sub-nodes,are selected. Node 55, as the highest node, denotes the case where all 6RBs, i.e., RB0 10 to RB5 15, are selected.

According to the compressed resource allocation expression method, whenthe number of RBs is N_(RB) ^(UL), the number of cases for selectingN_(RB) ^(UL)−k RBs is (k+1), where k=0, 1, . . . , N_(RB) ^(UL).Accordingly, the number of cases for resource allocation can beexpressed as shown in Equation (1).

$\begin{matrix}{{\sum\limits_{k = 0}^{N_{RB}^{UL}}\left( {1 + k} \right)} = \frac{N_{RB}^{UL}\left( {N_{RB}^{UL} + 1} \right)}{2}} & (1)\end{matrix}$

In Equation (1), the number of bits required for an uplink resourceallocation field is |log₂ (N_(RB) ^(UL)(N_(RB) ^(UL)+1)/2)|.

Because the information carried by the DCI format 0 and 1A differ fromeach other, the numbers of bits of the formats 0 and 1A are likely to bedifferent from each other. Further, because the sizes of the formats 0and 1A should be equal to each other, Z₀ padding bits are appended toformat 0. The padding bits are zero bits. How to determine Z₀ will bedescribed later in more detail.

The DCI format 1A is a DL-DCI using the same compressed resourceallocation expression as DCI format 0 and includes the informationfields as shown in Table 3 below.

TABLE 3 Field Number of bits C-RNTI 16 Format 0/format 1Adifferentiation 1 flag Distributed resource allocation flag 1 Resourceallocation$\left\lceil {\log_{2}\left( \frac{N_{RB}^{DL}\left( {N_{RB}^{DL} + 1} \right)}{2} \right)} \right\rceil$MCS 5 HARQ process number 3 for FDD, 4 for TDD NDI 1 RV 2 TPC command 2DL subframe index 0 in FDD mode, 2 in TDD mode Padding bits appended toformat 0 Z_(1A) Padding bits appended to avoid the 1 when the sizebelongs to one of size from belonging to one of ambiguous sizes,otherwise 0. ambiguous sizes

In Table 3, the format 0/format 1A differentiation flag is 1 bit, whichis set to 0 to indicate format 0 and set to 1 to indicate format 1A. Thedistributed resource allocation flag is 1 bit, which is used in similarmanner to the frequency hopping flag, to indicate whether the downlinkresource is allocated in distributed manner.

In order to achieve diversity gain, it is preferable to use thedistributed resource allocation. Because the downlink data transmissionis performed in asynchronous HARQ, the individual 5-bit MCS and 2-bit RVfields are defined, and an HARQ process number field is added toidentify the HARQ process. The HARQ process number field is 3 bits inFDD mode and 4 bits in TDD mode.

Because the DCI format 0 and DCI format 1A carry different information,the number of information bits in each of the DCI formats 0 and 1A islikely to be different from each other. However, because DCI formats 0and 1A should in the same size, Z_(1A) padding bits are appended to theDCI format 1A until the payload size is the same as format 0. If thenumber of information bits in format 1A is greater than that of format 0before appending the padding bits, Z₀=0.

The padding bits appended to format 1A are zero bits. Additionally, howto determine Z_(1A) will be described later in more detail.

Because the DCI format 0 is formed in similar manner, it is requiredthat a DCI format's payload size be determined first. For DCI format 1A,there is an additional step of appending one padding bit when thepayload size in format 1A, except for the 16-bit UE identifier, is anambiguous size. Accordingly, it is preferable to determine the payloadsize of format 1A first and then that of format 0. A method ofdetermining the payload sizes of DCI formats 0 and 1A will be describedin more detail below with reference to FIG. 3.

The payload size of format 1A should not be an ambiguous size because achannel coding rate of the PDCCH can be adjusted according to thechannel condition of the UE. That is, because the PDCCH is coded with afixed QPSK modulation scheme, adjusting the channel coding rate meansadjusting the frequency-time resource amount for transmitting the PDCCH.When a channel condition of the corresponding UE is good, it is possiblefor the UE to receive the PDCCH transmitted with small amount offrequency-time resource. However, when a channel condition of the UE isbad (e.g., when the UE is positioned at a cell boundary), the PDCCHshould be transmitted with a relatively large amount of frequency-timeresources. Because the amount of resources for the PDCCH is variable,the UE should estimate the resource amount allocated for the PDCCHtransmitted to itself. Accordingly, the UE performs blind decoding onthe PDCCH with potential resource amounts. If the payload size of DCIformat has a specific value, the PDCCH can be successfully decoded withmultiple potential resource amounts.

In order to avoid this problem, a padding bit is appended to forciblyincrease payload size, such that the payload size is not an ambiguoussize. The ambiguous payload sizes are a set S_(AS)={12, 14, 16, 20, 24,26, 32, 44 56}. That is, the number of information bits (payload size)of the DCI, except for the UE identifier, is ambiguous when it belongsto one of the set S_(AS)={12, 14, 16, 20, 24, 26, 32, 44, and 56}. Whenthe number of information bit is one of 12, 14, 16, 20, 24, 26, 32, 44,and 56, a padding bit is appended to the format.

For example, if a payload size of a DCI format is 24 bits, which is anambiguous size, a padding bit is appended to the DCI format, resultingin a 25 bit payload size. Because this problem occurs only in theDL-DCI, there is no need to consider this problem in the DCI format 0for the UL-DCI.

In DCI format 1A, the value of the resource allocation field isdetermined depending on the downlink bandwidth. When the number ofdownlink RBs is N_(RB) ^(DL), the resource allocation field is set to|log₂ (N_(RB) ^(DL)(N_(RB) ^(DL)+1)/2)|.

As described above, in LTE, an OFDMA scheme is used for downlinktransmission. Therefore, there is no need to consider the constraint ofconsecutive RBs allocation for reducing PAPR. However, because adoptingthe constraint reduces the number of bits for indicating resourceallocation, it is preferred to use the same method used in the DCIformat 0 when the compressed resource allocation expression is used asthe DCI format 1A. It is noted that the number of bits required forresource allocation is determined by N_(RB) ^(DL) because the uplink anddownlink bandwidth may differ from each other in the LTE system.

Unlike the DCI format 1A, the DCI format 1 is a DL-DCI that does not usethe compressed allocation expression method and includes the informationfields as shown in Table 4 below.

TABLE 4 Field Number of bits C-RNTI 16 Resource allocation header 0 ifDL bandwidth ≦ 10 RBs, otherwise 1 Resource allocation$\left\lceil \frac{N_{RB}^{DL}}{P} \right\rceil$ MCS 5 HARQ processnumber 3 for FDD, 4 for TDD NDI 1 RV 2 TPC command 2 DL subframe index 0in FDD mode, 2 in TDD mode Padding bits appended to format 1 when equalto format 0/1A, 0/1A otherwise 0 Padding bits appended to avoid the 1when the size belongs to one of size from belonging to one of ambiguoussizes, otherwise 0 ambiguous sizes

In Table 4, the DCI format 1 differs from the DCI format 1A in threeaspects. First, the format 1 does use a bit for a format 0/1Adifferentiating flag because the format 1 is different from the format0/1A in payload size. In order to avoid the format 1 having the samepayload size as the format 0/1A, a number of padding bits Z₁ is defined.If the payload size of format 1 differs from that of format 0/1A, Z₁=0.

Instead of a 1-bit distributed resource allocation flag, the format 1includes a 1-bit resource allocation header. Because the DCI format 1has no constraint on consecutive RB allocation, there is no need todefine the distributed resource allocation. The 1-bit resourceallocation header is used to indicate a group resource allocation typeor a subset resource allocation type. If the downlink bandwidth is lessthan or equal to 10 RBs, there is no difference between the two resourceallocation type, thereby no resource allocation is required.

Hereinbelow, the group resource allocation method is described withreference to FIG. 2, but the detailed description about the subsetresource allocation method is omitted since the two types of resourceallocation methods use the same number of bits to indicate the allocatedresource and the resource allocation is outside of the scope of thepresent invention.

Finally, format 1 differs from format 1A in resource allocation method.As described above, format 1A has a constraint of consecutive RBsassignment, but format 1 can express the resource allocation in morediverse ways by introducing other constraints.

FIG. 2 is a diagram illustrating a principle of a group resourceallocation method supported in DCI format 1.

Referring to FIG. 2, the downlink bandwidth includes 25 RBs (RB0 10 toRB24 24). In order to assign resources in a unit of an RB, a 25-bitbitmap is defined. Similarly, when 100 RBs are defined, 100-bit bitmapis required. Accordingly, the bitmap method is inefficient as thebandwidth increases. In order to solve this problem, a group resourceallocation method is introduced.

Referring to FIG. 2, node 101 denotes a resource block group includingRB0 10 and RB1 11. Nodes 101, 103, 105, and 107 are bitmaps indicatingcorresponding resource block groups. For example, if the first andsecond bits are set to 1, nodes 101 and 103 are selected to assign theRB0 10, RB1 11, RB12 12, and RB13 13. Using the bitmap indication,non-consecutive resource allocation is possible. For example, byselecting node 101 and node 105, four non-consecutive resource blocks(RB0 10, RB1 11, RB22 22, and RB23 23) can be assigned.

In the example illustrated in FIG. 2, a group size P is 2. In order toprevent a size of a bitmap from increasing in proportion to the numberof RBs, the group size can be increased at increasing intervals, as thenumber of RBs increases. An example of the group size P being determineddepending on the number of RBs is shown below in Table 5.

TABLE 5 N_(RB) ^(DL) Group size, P ≦10 1 11~26 2 27~63 3  64~110 4

In Table 5, the size of resource allocation bitmap is determineddepending on the number of groups. If the number of downlink RBs isN_(RB) ^(DL) and the group size is P, the size of bitmap is |N_(RB)^(DL)/P|.

DCI format 1 supports a subset resource allocation method as well as thegroup resource allocation method. The number of bits of the resourceallocation field is |N_(RB) ^(DL)/P| in both the resource allocationmethods. A detailed description of the subset resource allocation methodis omitted in the present application.

The present invention is directed to a method for solving the problemrelated to differentiation between the DCI formats 0, 1, and 1A.Therefore, descriptions of the other DCI formats listed in Table 1 arenot presented herein.

FIG. 3 is a flowchart illustrating a procedure of determining payloadsizes of DCI formats 0, 1, and 1A in a downlink control informationtransmission method according to an embodiment of the present invention.The payload size determination procedure of FIG. 3 can be performed in apayload controller of a downlink control channel transmitter.

Because the DCI formats 0 and 1A have the same payload size and thepayload size of the DCI format 1A is not an ambiguous size, the payloadsizes of the DCI formats 0 and 1A are determined through the payloadsize determination procedure illustrated in FIG. 3.

In FIG. 3, the payload size of the DCI format 0 is N₀, and the payloadsize of the DCI format 1A is N_(1A).

A payload controller determines the payload size N_(1A) of the DCIformat 1A in step 201. The payload size N_(1A) of the DCI format 1A isdetermined depending on the downlink bandwidth (i.e., the number of RBs)and the duplex mode as described in Table 3. The padding bits and 16-bitUE identifier are excluded from determining the payload size N_(1A).

In step 203, the payload controller determines the payload size N₀ ofthe DCI format 0. The payload size N₀ of the DCI format 0 is determineddepending on the uplink bandwidth (i.e., the number of uplink RBs) andthe duplex mode as described in Table 2. Here, the padding bits and16-bit UE identifier are also excluded from determining the payload sizeN₀.

Once the payload sizes N_(1A) and N₀ are determined, the payloadcontroller compares the payload size N_(1A) of DCI format 1A and thepayload size N₀ of DCI format 0 to determine whether the payload sizeN_(1A) of the DCI format 1A is less than the payload size N₀ of the DCIformat 0 in step 205. Because a padding bit can be appended to the DCIformat 1A to avoid the payload size of the DCI format 1A being anambiguous size, the payload controller determines the payload size N₀ ofthe DCI format 1A first and then the DCI format 0 in consideration ofthe payload size N_(1A) of the DCI format 1A. The payload sizecomparison at step 205 is performed to determine the number of paddingbits to be appended when the payload size N_(1A) calculated at step 201is less than the payload size N₀ calculated at 203.

More specifically, if N_(1A)<N₀, in step 207, the payload controllercalculates the number of padding bits (Z_(1A)=N₀−N_(1A)) to append tothe DCI format 1A and updates the payload size of the DCI format 1A asN_(1A)=N_(1A)+Z_(1A), such that N₀=N_(1A). However, if N_(1A)≧N₀, step207 is skipped.

In step 209, the payload controller determines whether the updatedpayload size N_(1A) of the DCI format 1A is an ambiguous size (S_(AS)).As described above, the S_(AS) is a set of ambiguous payload sizes. Ifthe payload size N_(1A) of the DCI format 1A is an ambiguous size, instep 211, the payload controller appends a padding bit to the DCI format1A and, subsequently, updates the N_(1A) as N_(1A)=N_(1A)+1. However, ifthe payload size N_(1A) is not an ambiguous size, step 211 is skipped.

The payload size N_(1A) of the DCI format 1A is finally determined as aresult of steps 209 and 211.

When the payload size N₀ of DCI format 0 calculated is less than thepayload size N_(1A) of the DCI format 1A at step 205, and step 207 isskipped, this state is maintained.

When the payload size N_(1A) of the DCI format 1A is less than thepayload size N₀ of the DCI format 10 in steps 205 and 207, the payloadsize N_(1A) of the DCI format 1A is forcibly equaled to the payload sizeN₀ of DCI format 0. However, the payload size N_(1A) of the DCI format1A is likely to be greater than the payload size N₀ of the DCI format 0through steps 209 and 211. Because the payload sizes of the DCI formats0 and 1A should be the same, the payload size N₀ of the DCI format 0must be equal to the payload size N_(1A) of the DCI format 1A.

Accordingly, the payload controller compares the finally acquired N_(1A)with N₀ to determine whether the N₀ is less than N_(1A) in step 213. IfN₀ is less than N_(1A), in step 215, the payload controller appends anumber of padding bits (Z₀:=N_(1A)−N₀) to the DCI format 0 and updatesthe payload size N₀ of format 0 as N₀:=N₀+Z₀, such that N₀=N_(1A).

In step 217, the payload controller completes the determination of thepayload sizes N₀ and N_(1A) of the DCI formats 0 and 1A satisfying thecondition N₀=N_(1A), while N_(1A) is not an ambiguous size.

FIG. 4 is a flowchart illustrating a procedure of determining payloadsize of DCI format 1 in a downlink control information transmissionmethod according to an embodiment of the present invention.

Referring to FIG. 4, in step 401, the payload controller determines thepayload size N₀ of the DCI format 0 and the payload size N_(1A) of theDCI format 1A in consideration of padding bits. The payload sizes N₀ andN_(1A) are determined to be equal to each other according to theprocedure of FIG. 3.

In step 403, the payload controller determines the payload size N₁ ofthe DCI format 1. The payload size N₁ of the DCI format 1 is determineddepending on the downlink bandwidth (i.e., the number of RBs) and duplexmode as described in Table 4. The padding bits and 16-bit UE identifierare excluded from determining the payload size N₁.

As described above, the payload size of the DCI format 1 must differfrom the payload size of the DCI format 0/1A. Accordingly, in step 405,the payload controller compares the payload size N₁ with the payloadsize N₀ to determine whether the N₁ is equal to N₀. If the N₁ is equalto N₀, in step 407, the payload controller appends one padding bit tothe DCI format 1 to differentiate the payload sizes and updates thepayload size N1 (N1:=N1+1). Otherwise, if N₁ is not equal to N₀, step407 is skipped.

In step 409, the payload controller determines whether the updatedpayload size N₁ of the DCI format 1 is an ambiguous size S_(AS). Asdescribed above, the S_(AS) is a set of ambiguous payload sizes.

If the payload size N₁ of the DCI format 1 is not an ambiguous size, instep 411, the payload controller appends padding bits to the DCI format1 until the payload size of the DCI format 1 is not an ambiguous sizeand is not equal to the payload size of the DCI format 0/1A. That is,the payload controller appends k padding bit(s) to the DCI format 1 andupdates N₁:=N₁+k, where k is the smallest positive integer thatsatisfies the conditions that the payload size of the DCI format 1 isnot an ambiguous size and is not equal to the payload size of the DCIformat 0/1A. Otherwise, if the payload size N₁ of the DCI format 1 doesnot belong to one of the ambiguous sizes, step 411 is skipped.

In step 413, the payload controller completes the determination of thepayload size N1 of DCI format 1.

Appending a padding bit to the DCI format 1 to avoid the payload size ofthe DCI format 1 from belonging to one of the ambiguous bits may cause aproblem in which the payload size of the DCI format 1 equals to thepayload size of the DCI format 0/1A. In order to prevent this problemfrom occurring, the format 1 payload size determination procedure inaccordance with an embodiment of the present invention appends paddingbits to the DCI format 1 until the payload size of the DCI format 1 isnot an ambiguous size and is also not equal to the payload size of theDCI format 0/1A. At this time, k padding bit(s) is appended to the DCIformat 1, and k is the smallest positive integer that satisfies theconditions that the payload size of the DCI format 1 is not an ambiguoussize and is not equal to the payload size of the DCI format 0/1A.

The number of bits of the payload is adjusted because, where the N₀ andN₁ have a relationship of N₁=N₀−1, and N₁ is an ambiguous size,incrementing N₁ by 1 (N₁=N₁+1) by appending a padding bit results inN₀=N₁. In order to avoid this problematic situation, another padding bitcan be appended, i.e., N₁+2. However, appending two padding bits mayalso can make the payload size an ambiguous size. Among the ambiguoussizes, i.e., S_(AS)={12, 14, 16, 20, 24, 26, 32, 44, and 56}, there arethe three subsets, (12, 14), (14, 16), and (24, 26), each having twoelements of which a difference is 2. Therefore, two padding bitsappended to the format 1 to avoid the problem caused by the one paddingbit addition may cause an ambiguous size problem.

In this situation, three padding bits can solve the ambiguous sizeproblem. That is, the number of padding bits to be appended to theformat 1 to avoid the payload size of the format 1 being an ambiguoussize can be 1, 2, or 3 depending on the situation. The payload sizedetermining procedure for the DCI format 1 according to an embodiment ofthe present invention allows an optimal number of padding bits inconsideration of various situations, thereby preventing a decoding errorat UE.

FIG. 5 is a block diagram illustrating a configuration of a downlinkcontrol channel transmitter of a base station in a wirelesscommunication system according to an embodiment of the presentinvention.

Referring to FIG. 5, the downlink control channel transmitter includes apayload size calculator 501, a scheduler 503, a PDCCH payload generator505, a channel encoder 507, a modulator 509, a PDCCH mapper 511, amultiplexer (MUX) 515, an OFDM signal generator 517, and a RadioFrequency (RF) transmitter 519. The payload size calculator 501calculates the payload size of DCI formats through the payload sizedetermination algorithm according to an embodiment of the presentinvention. That is, the payload controller 510 performs the procedureillustrated in FIG. 4 to determine the number of bits of the payload ofthe PDCCH. The scheduler 503 controls generation of control informationand mapping the control information to the PDCCH. The PDCCH payloadgenerator 505 generates the control information to be transmitted on thePDCCH, based on the payload size output by the payload controller 501under the control of the scheduler 503.

The channel encoder 507 performs channel coding on the PDCCH payload ina predetermined coding scheme. The modulator 509 performs modulation onthe channel-coded signal in a predetermined modulation scheme.

The multiplexer 515 multiplexes the PDCCH containing control informationand other channels (e.g., PDCCH). The OFDM signal generator 517transforms the multiplexed signal output by the multiplexer 515 intoOFDM signal, and the RF transmitter 519 converts the OFDM signal outputby the OFDM signal generator 517 into a predetermined transmission bandfrequency and transmits the radio frequency signal over the air.

More specifically, the payload controller 501 determines payload sizesN₀ and N_(1A) (N₀=N_(1A)) of the DCI formats 0 and 1A and then N₁ of theDCI format 1 in consideration of the N₀ (=N_(1A)) as described withreference to FIG. 3. The payload size of the DCI format 1 is determineddepending on the downlink bandwidth (i.e., the number of RBs) and duplexmode as described in Table 4. As described above, the padding bits and16-bit UE identifier are excluded from determining the payload size N₁.Because the payload size of the DCI format 1 must not be equal to thatof the DCI format 0/1A, the payload controller 501 compares N₁ with N₀and, if N₁ is equal to N₀, appends a padding bit to the DCI format 1 andupdates N₁ (N₁=N₁+1). Otherwise, if N₀ is not equal to N₁, the payloadcontroller 501 skips the padding bit appending process.

Next, the payload controller 501 determines whether the payload size N₁of the DCI format 1 is an ambiguous size and, if the payload size N₁ isan ambiguous size, appends padding bits to the DCI format 1 until thepayload size is not an ambiguous size. At this time, the payloadcontroller appends k padding bit(s) to the DCI format 1, where k is thesmallest positive integer that satisfies the conditions that the payloadsize of the DCI format 1 is not an ambiguous size and is not equal tothe payload size of the DCI format 0/1A. However, if the payload size N₁of the DCI format 1 is not an ambiguous size, the payload controller 501skips the padding bit addition process.

Once the payload size calculation has completed, the payload controller501 determines payload size N1 of the DCI format 1 and informs thepayload generator 505 of the payload size N1 of the DCI format 1.

Once the payload size of the DCI format is determined by the payloadcontroller 501, the payload generator 505 inserts the controlinformation into the payload of the PDCCH.

In PDCCH, the number of zero padding bits is determined depending on thepayload size, such that the payload generator 505 generates the payloadusing the payload size calculated by the payload controller 501. Thecontrol information to be carried by the PDCCH is determined by thescheduler 503. That is, the scheduler 503 allocates resources to the UEand controls the payload generator 505 that is responsible forgenerating the payload and the PDCCH mapper 511 that is responsible formapping the PDCCH to the frequency-time resources allocated per user.

Once all the information of the PDCCH is defined, the PDCCH informationis encoded by the channel encoder 507 and then modulated by themodulator 509 into QPSK signal. The modulation signal is output to thePDCCH mapper 511 in order to be mapped to the frequency-time resourcesallocated per user. The PDCCH signal is multiplexed with other channelsby the multiplexer 515 and then converted into the OFDM signal by theOFDM signal generator 517. Finally, the OFDM signal is converted intoradio frequency signal and then transmitted through a transmissionantenna 512.

FIG. 6 is a block diagram illustrating a configuration of a downlinkcontrol channel receiver of a UE in a wireless communication systemaccording to an embodiment of the present invention.

Referring to FIG. 6, the downlink control channel receiver includes anRF receiver 603, an OFDM signal receiver 605, a PDCCH demapper 607, ademodulator 609, a payload size calculator 611 and a channel decoder613. The RF receiver 603 converts the RF signal received through antenna601 into a baseband signal. The OFDM signal receiver 605 recovers thefrequency-time signals from the baseband signal. The PDCCH demapper 607performs demapping on the signal output by the OFDM signal receiver 605to recover the signal mapped to the PDCCH. The demodulator 609demodulates the signal demapped by the PDCCH demapper 607. The payloadsize calculator 611 calculates the payload size for DCI format of thereceived PDCCH according to an exemplary embodiment of the presentinvention. The channel decoder 613 performs decoding on the signaloutput by the demodulator 609 based on the payload size calculated bythe payload size calculator 611.

More specifically, the RF signal received through the antenna 601 isconverted into a base band signal by the RF receiver 603 and thenrecovered to a frequency-time signal by the OFDM signal receiver 605.The frequency-time signal is demapped by the PDCCH demapper 607 anddemodulated by the demodulator 609 so as to be output in the form of aPDCCH. The channel decoder 613 must know the payload size of the DCIformat for channel decoding. Accordingly, the payload controller 611calculates the payload size of the DCI format and outputs the calculatedpayload size to the channel decoder 613. The channel decoder 613 thenperforms decoding on the PDCCH, based on the payload size calculated bythe payload controller 611. Therefore, the downlink control channelreceiver of the UE can acquire the control information carried by thePDCCH.

Because the payload size of the DCI format 1 is differentiated from thatof the DCI format 0/1A, i.e., the different DCI formats have differentpayload sizes, the downlink control channel receiver can differentiatethe DCI format 1 from the DCI format 0/1A. Accordingly, the UE cancorrectly process the PDCCH based on the DCI format of the PDCCH.

The payload controller 501 of the downlink control channel transmitterof base station and the payload controller 611 of the downlink controlchannel receiver of UE can each be implemented with a memory. In thiscase, the payload size of each DCI formation can be calculated withreference to the uplink and downlink bandwidths and duplex modeinformation, and then stored in the memory (base station downlinkcontrol information transmitter 501 and UE downlink control informationreceiver 611) and provided, if requested, to the payload generator 505of the downlink control information transmitter 50 and the channeldecoder 613 of the downlink control information receiver.

Although the payload controller 501 of the downlink control informationtransmitter 501 of the base station and the payload controller 611 ofthe downlink control information receiver of the UE can be replaced bymemories, the payload size of DCI format 1 stored in the memory must becalculated through the payload size determination procedure according toan embodiment of the present invention.

As described above, the downlink control information transmission deviceand apparatus in accordance with the embodiments of the presentinvention enable efficient payload size differentiating of DCI format 1from that of DCI format 0/1A, thereby improving PDCCH decodingperformance at UE.

Also, the downlink control information transmission device and apparatusof the present invention first determine the payload size of the DCIformat 0/1A and DCI format 1 and, if the payload size of the DCI format1 is an ambiguous size, appends padding bits to the DCI format 1 untilthe payload size of the DCI format 1 is not an ambiguous size and is notequal to the payload size of the DCI format 0/1A, such that the UE candifferentiate the DCI formats of the downlink control information basedon the payload size, resulting in improvement of PDCCH processingstability.

Although various embodiments of the present invention have beendescribed in detail hereinabove, it should be clearly understood thatmany variations and/or modifications of the basic inventive conceptstaught herein will still fall within the spirit and scope of the presentinvention, as defined in the appended claims and their equivalents.

What is claimed is:
 1. A method for a transmitter in a communication system, the method comprising: identifying, by a transmitter, information bits in a first downlink control information (DCI) and information bits in a second DCI; appending, by the transmitter, one bit of value zero to the second DCI, if a number of the information bits in the second DCI is equal to a number of the information bits in the first DCI; appending, by the transmitter, one or more zero bits to the second DCI based on a payload size of the second DCI, if the number of the information bits in the second DCI belongs to one of ambiguous sizes; and transmitting, to a receiver, the second DCI, wherein a payload of the second DCI comprises the information bits in the second DCI and at least one zero padding bit appended to the second DCI, wherein the one or more zero bits are appended to the second DCI until the payload size of the second DCI does not belong to one of the ambiguous sizes and the payload size of the second DCI is not equal to a payload size of the first DCI, and wherein the transmitted second DCI is received based on the payload size of the second DCI.
 2. The method of claim 1, wherein the ambiguous sizes comprise one of 12, 14, 16, 20, 24, 26, 32, 44, and 56 information bits.
 3. The method of claim 1, wherein the first DCI comprises a DCI format 0 and a DCI format 1A and the second DCI comprises a DCI format 1, and wherein identifying the information bits in the first DCI and the information bits in the second DCI comprises: appending at least one zero bit to the DCI format 1A until the payload size of the DCI format 1A equals the payload size of the DCI format 0, if a number of information bits in the DCI format 1A is less than a number of information bits in the DCI format 0; and appending one zero bit to the DCI format 1A, if the number of the information bits in the DCI format 1A belongs to one of the ambiguous sizes.
 4. The method of claim 3, wherein identifying the information bits in the first DCI and the information bits in the second DCI further comprises: appending at least one zero bit to the DCI format 0 until the payload size of the DCI format 0 equals the payload size of the DCI format 1A, if the number of the information bits in the DCI format 0 is less than the payload size of the DCI format 1A.
 5. A method for a receiver in a communication system, the method comprising: receiving, by a receiver from a transmitter, control information comprising at least one of a first downlink control information (DCI) and a second DCI; and decoding, by the receiver, the control information based on a payload size of the second DCI, wherein one bit of value zero is appended to the second DCI by the transmitter, if a number of information bits in the second DCI is equal to a number of information bits in the first DCI, wherein a payload of the second DCI comprises the information bits in the second DCI and at least one zero padding bit appended to the second DCI, wherein one or more zero bits are appended to the second DCI based on the payload size of the second DCI by the transmitter, if the number of the information bits in the second DCI belongs to one of ambiguous sizes, and wherein the one or more zero bits are appended to the second DCI until the payload size of the second DCI does not belong to one of the ambiguous sizes and the payload size of the second DCI is not equal to a payload size of the first DCI.
 6. The method of claim 5, wherein the ambiguous sizes comprise one of 12, 14, 16, 20, 24, 26, 32, 44, and 56 information bits.
 7. The method of claim 5, wherein the first DCI comprises a DCI format 0 and a DCI format 1A and the second DCI comprises a DCI format 1, wherein at least one zero bit is appended to the DCI format 1A until the payload size of the DCI format 1A equals the payload size of the DCI format 0 by the transmitter, if a number of information bits in the DCI format 1A is less than a number of information bits in the DCI format 0, and wherein one zero bit is append to the DCI format 1A by the transmitter, if the number of the information bits in the DCI format 1A belongs to one of the ambiguous sizes.
 8. The method of claim 7, wherein at least one zero bit is appended to the DCI format 0 until the payload size of the DCI format 0 equals the payload size of the DCI format 1A by the transmitter if the number of the information bits in the DCI format 0 is less than the payload size of the DCI format 1A.
 9. A transmitting apparatus in a communication system, the apparatus comprising: a transmitter for transmitting a signal to a receiver; and a controller coupled to the transmitter and configured to: identify information bits in a first downlink control information (DCI) and information bits in a second DCI, append one bit of value zero to the second DCI, if a number of the information bits in the second DCI is equal to a number of the information bits in the first DCI, append one or more zero bits to the second DCI based on a payload size of the second DCI, if the number of the information bits in the second DCI belongs to one of ambiguous sizes, and transmit, to a receiver, the second DCI, wherein a payload of the second DCI comprises the information bits in the second DCI and at least one zero padding bit appended to the second DCI, wherein the one or more zero bits are appended to the second DCI until the payload size of the second DCI does not belong to one of the ambiguous sizes and the payload size of the second DCI is not equal to a payload size of the first DCI, and wherein the transmitted second DCI is received based on the payload size of the second DCI.
 10. The apparatus of claim 9, wherein the ambiguous sizes comprise one of 12, 14, 16, 20, 24, 26, 32, 44, and 56 information bits.
 11. The apparatus of claim 9, wherein the first DCI comprises a DCI format 0 and a DCI format 1A and the second DCI comprises a DCI format 1, and wherein the controller is further configured to append at least one zero bit to the DCI format 1A until the payload size of the DCI format 1A equals the payload size of the DCI format 0 if a number of information bits in the DCI format 1A is less than a number of information bits in the DCI format 0 and to append one zero bit to the DCI format 1A if the number of the information bits in the DCI format 1A belongs to one of the ambiguous sizes.
 12. The apparatus of claim 11, wherein the controller is further configured to append at least one zero bit to the DCI format 0 until the payload size of the DCI format 0 equals the payload size of the DCI format 1A if the number of the information bits in the DCI format 0 is less than the payload size of the DCI format 1A.
 13. A receiving apparatus in a communication system, the apparatus comprising: a receiver for receiving a signal from a transmitter; and a controller coupled to the receiver and configured to: receive, from a transmitter, control information comprising at least one of a first downlink control information (DCI) and a second DCI, and decode the control information based on a payload size of the second DCI, wherein one bit of value zero is appended to the second DCI by the transmitter, if a number of information bits in the second DCI is equal to a number of information bits in the first DCI, wherein a payload of the second DCI comprises the information bits in the second DCI and at least one zero padding bit appended to the second DCI, wherein one or more zero bits are appended to the second DCI based on the payload size of the second DCI by the transmitter, if the number of the information bits in the second DCI belongs to one of ambiguous sizes, and wherein the one or more zero bits are appended to the second DCI until the payload size of the second DCI does not belong to one of the ambiguous sizes and the payload size of the second DCI is not equal to a payload size of the first DCI.
 14. The apparatus of claim 13, wherein the ambiguous sizes comprise one of 12, 14, 16, 20, 24, 26, 32, 44, and 56 information bits.
 15. The apparatus of claim 13, wherein the first DCI comprises a DCI format 0 and a DCI format 1A and the second DCI comprises a DCI format 1, wherein at least one zero bit is appended to the DCI format 1A until the payload size of the DCI format 1A equals the payload size of the DCI format 0 by the transmitter if a number of information bits in the DCI format 1A is less than a number of information bits in the DCI format 0, and wherein one zero bit is append to the DCI format 1A by the transmitter if the number of the information bits in the DCI format 1A belongs to one of the ambiguous sizes.
 16. The apparatus of claim 15, wherein at least one zero bit is appended to the DCI format 0 until the payload size of the DCI format 0 equals the payload size of the DCI format 1A by the transmitter if the number of the information bits in the DCI format 0 is less than the payload size of the DCI format 1A. 